Method for adjusting a lamp relative to an illuminating beam path of a microscope and a microscope suitable for carrying out the method

ABSTRACT

The invention relates to a method for automatic lamp adjustment in a microscope without beam homogenizers in the illuminating beam path and a microscope equipped for the application of the method. According to the invention, the light power in the illuminating beam path is integrally measured with a detector behind the pupil plane of the microscope objective or behind the pupil plane of the illuminating beam path and the lamp is so adjusted relative to the illuminating beam path that the light power, which is detected by the detector, is a maximum. In a microscope, which is suitable for an automated lamp adjustment, for example, after an exchange of the lamp according to the method of the invention, motorized drives are provided for adjusting the lamp. These drives are driven sequentially by an evaluation and control computer until a maximum light power is detected with a detector.

FIELD OF THE INVENTION

The invention relates to a method for adjusting a lamp relative to anilluminating beam path of a microscope without a beam homogenizer and amicroscope suitable for carrying out the method.

BACKGROUND OF THE INVENTION

The adjustment of lamps for microscope illumination takes place usuallyin accordance with classical adjustment criteria which ensure ahomogeneous illumination of the object field. This applies to the firstadjustment of a microscope as well as to an exchange of a lamp. A firstadjustment criterion is a sharp imaging of the light source, that is, ofthe light arc or of the lamp filament into the pupil of the objective.This adjustment criterion can be checked with the aid of a so-calledBertrand lens which images the objective pupil in the viewing field ofthe microscope. In lieu of a visual control of the sharp imaging, a CCDcamera can be mounted in the image plane of the Bertrand lens and theimage of the CCD camera is evaluated as to a sharpness of imaging. As asecond criterion, the illumination in the object field itself can bechecked as to homogeneity and, if necessary, the lamp is readjusted tomaximum homogeneity. The object of lamp adjustment is to always ensure asubstantially homogeneous illumination in the object field.

Because of the complexity of these classical methods for lampadjustment, these methods are suited only to a limited extent to anautomatization (in the first assembly and also after an exchange oflamps) in such a manner that the microscope ensures a homogeneousillumination of the object field without manual intervention. On theother hand, experience has shown that especially routine users ofmicroscopes are often unable to make a lamp adjustment in accordancewith classical adjustment criteria.

Beam homogenizers are used in illuminating devices for microlithographicapparatus and these illuminating devices ensure a homogeneousillumination of the mask to be imaged. Additionally, the position of thelight source relative to the illuminating beam path is adjusted tomaximum light power of the beam homogenizer so that the light poweremitted by the light source is optimally utilized.

It would be conceivable to utilize beam homogenizers also for microscopeillumination, for example, in the form of so-called fly-eye lenses orglass rods for mixing light. A homogeneous illumination of the objectfield would thereby be guaranteed independently of the positioning ofthe lamp relative to the illuminating beam path so that one could docompletely without a lamp adjustment. The use of such beam homogenizerswould, however, lead to a complexity in microscopes which could not berealized.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the invention to provide asimple method for lamp adjustment in microscopes which ensures ahomogeneous illumination of the object field to be illuminated and iswell suited to automatization. A further object of the invention is toprovide a microscope which, when utilizing the method of the invention,is suitable to bring about an adjustment of the lamp automatically whichensures a homogeneous illumination of the object field.

The method of the invention is for adjusting a lamp unit relative to anilluminating beam path of a microscope devoid of a beam homogenizer inthe illuminating beam path. The microscope includes: a microscopeobjective defining a pupil plane; an adjustable lamp unit for supplyingthe light transmitted along the illuminating beam path and a detectorfor detecting the light power of the transmitted light. The methodincludes the steps of: measuring the integral light power downstream ofthe pupil plane of the objective with the detector; and, adjusting thelight unit relative to the illuminating beam path so that the lightpower detected by the detector is a maximum.

The invention is based on the recognition that a homogeneousillumination of the illuminated field is guaranteed also forilluminating beam paths without beam homogenizers when the areallyintegral light power behind the pupil plane of the microscope objectiveor behind the pupil plane of the illuminating beam path is a maximumwith the operating conditions of the lamp being otherwise constant.Correspondingly, in the method according to the invention, the areallyintegral light power behind the pupil plane of the microscope objectiveor behind the pupil plane of the illuminating beam path is measured by adetector and the lamp body is so adjusted relative to the illuminatingbeam path that the integral light power, which is detected with thedetector, is a maximum. What is here important is that the integraldetection of the light power takes place only after passing through thediaphragm delimiting the light flow.

Based on the recognition of the invention, a simple adjustment criterionis provided which is exceptionally well suited for the automatedadjustment of the lamp after a lamp exchange or for the automatedadjustment of the lamp in a first adjustment. The adjustment of the lampcan be motor controlled via software. The realization of the inventionis, however, also usable in the manual adjustment of the lamp becausethe adjustment criterion of a maximum integral light power can bechecked much more simply by the inexperienced operator than theconventional adjusting criterion of a sharp imaging of a lamp arc in theobjective pupil by means of a Bertrand lens.

A microscope, which is suitable for automatic lamp adjustment, includesmotorized drives for adjusting the lamp relative to the illuminatingbeam path as well as an evaluation and control computer. The motorizeddrives operate to displace optical components in the illuminating beampath and this beam path is without beam homogenizers. The evaluation andcontrol computer sequentially controls the motorized drives for lampadjustment in such a manner until a maximum of the integral light poweris measured by a detector mounted behind the pupil plane of theilluminating beam path or of the microscope objective.

The detector for detecting the light power can be integrated into theilluminating beam path. In this case, it is advantageous when areflecting region is provided on the specimen table of the microscopeand when the detector detects the light reflected at the reflectingregion. Alternatively, a portion of the illuminating beam path can bereflected out onto a detector.

Furthermore, it is possible to provide the detector for detecting thelight power more or less open on the specimen table. This embodiment isespecially suitable for retrofitting already existing microscopes aswell as for use of the invention within already existing series ofmicroscopes.

The following are all suitable as a detector: an individual diode, afour-quadrant diode or even a CCD camera. In the case of a quadrantdiode or a CCD sensor, the light power, which is detected with theindividual sensor parts or sensor regions, is integrated over an area atthe detector output. The use of a CCD sensor or a CCD camera isespecially considered when, for example, a CCD camera is anyway providedfor image documentation as, for example, in reflected light microscopes.

For applying the invention, the lamp can be adjusted either in threemutually orthogonal spatial directions relative to the illuminating beampath or, it is also possible, to adjust the lamp only in two mutuallyperpendicular spatial directions and a collector optic, which isarranged in the beam path, is displaceable along the optical axis of theremaining illuminating beam path.

A gradient method can preferably be used for locating the maximum lightpower. In such a gradient method, and starting from an initial position,the maximum gradient of the light power is determined in dependence upona position change of the lamp relative to the illuminating beam pathand/or the lamp and the collector optic relative to the illuminatingbeam path and, thereafter, the lamp and/or the collector optic isshifted in the direction of the maximum gradient of the light power inthe illuminating beam path.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 is a reflected light microscope, in section, having a detectorintegrated in the specimen table;

FIG. 2 is a flowchart of the process steps which are run through withthe automated lamp adjustment in a microscope;

FIG. 3 is a flowchart of the process steps which are run in the gradientmethod for locating the maximum light power; and,

FIG. 4 shows a microscope, in section, having a detector integrated intothe illuminating beam path.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, the upper part of the microscope stand with the illuminatingbeam path accommodated therein is identified by reference numeral 1. Aspecimen table 2 adjustable in elevation for focusing is accommodated onthe microscope in a manner known per se. Furthermore, the microscopeincludes a lens turret 3 containing objectives 4 of which only one isshown in FIG. 1.

The reflecting illuminating beam path in the microscope of FIG. 1includes, in principle, the components which are usual for theadjustment of the Köhler illuminating conditions. A halogen lamp or agas discharge lamp 5 can be provided as a light source. The light, whichis emitted by the lamp 5, is collimated by a collector lens 9 and, ifrequired, is collimated in combination with a collector mirror 17 whichcollects the backward radiated light and reflects it back into the lamp5. A field diaphragm 10 is provided in the region of the collimated beampath and is adjustable with respect to its aperture diameter. The fielddiaphragm 10 is arranged conjugated to the focal plane of the microscopeobjective 4. A lens 11 is mounted downstream of the field diaphragm 10and images the field diaphragm 10 to infinity. A second diaphragm 12 isprovided in the focal plane of lens 11 for adjusting the illuminationaperture. The second diaphragm 12 is adjusted with respect to itsaperture diameter and is imaged to infinity by a downstream lens 13 and,after being reflected into the viewing beam path, the aperture diaphragm12 is imaged into the exit pupil 18 of the microscope objective 4 by thetube lens 15 via a beam splitter 14. The tube lens 15 is in the commonpart of the illuminating and viewing beam path.

A large area diode 16 is integrated as a detector in the specimen table2 of the microscope. With the diode 16, the total light intensityfocused by the microscope objective 4 is detected. This diode 16 can beconfigured as a simple large-area diode. However, it is especiallyadvantageous to configure the diode 16 as a four-quadrant diode. In thislast case, this diode 16 can thereby simultaneously function to alsocalibrate the specimen table in that the center point of thefour-quadrant diode defines the origin of the axes as a reference point,for example, as zero point for the X/Y adjustment of the specimen table.

The diameter of the light-sensitive area of the diode 16 is at least aslarge as the diameter of the field illuminated in the focal plane of theobjective 4. In a quadrant diode, the diameters of the four quadrantstogether are taken as the diameter.

For realizing an automated lamp adjustment, the receptacle or holder 8of the lamp 5 is adjustable by two motorized drives (6, 7) in the twodirections perpendicular to the optical axis 19 of the illuminating beampath. The collector lens 9 is displaceable in the direction of theoptical axis 19 by a further motorized drive 20. Alternatively to adisplacement of the lamp 5 as well as the collector lens 9, the lamp 5can also be displaceable via three appropriate drives in the threemutually perpendicular spatial directions. However, for this purpose, acorrespondingly more complex mechanism is required because of thedegrees of freedom which would be required for an adjustment in thethree mutually perpendicular directions independently of each other.

Position sensors provide input signals representing the end positions ofthe drives (6, 7, 20) so that information is provided to a computer 22as to the actual positions reached by the respective drives (6, 7, 20).Alternatively, the drives (6, 7, 20) can be step motors so that thedistance to be moved is known from the number of steps to be executed.

The adjusting drives (6, 7) of the lamp 5 and the adjusting drive 20 ofthe collector lens 9 are drivable by the control computer 22 across aninterface 21. The output signals of the diode 16 are supplied to thecontrol computer 22 over the same interface 21.

The method steps, which are run through for an automatic lampadjustment, are explained in greater detail in the following withrespect to FIG. 2. The adjusting process begins with an initial step 30which is, for example, triggered in that the user confirms a completedexchange of lamps via a key pad. In a next initialization step 31, thespecimen table 2 is moved in the direction of the optical axis of themicroscope objective 4 as well as in the two directions perpendicularthereto so that the diode 16 is positioned beneath the microscopeobjective 4 and, as a consequence, detects the total light power, whichis collected by the microscope objective 4. This initialization can, ofcourse, take place also automated if the microscope has a motorizedfocusing drive and a motorized X/Y table. In this case, the control andevaluation computer 22 correspondingly controls the motorized drives forthe focusing and the lateral position of the specimen table. If nomotorized drives for the focusing and the X/Y table are provided, thenthe user receives the command via the key pad to so adjust the specimentable that the diode 16 is positioned directly beneath the objective 4.

In the next two steps (32, 33), an assignment of a variable takes placewherein the value of a variable “new position” is assigned to a variable“old position” and the value of a variable “position a” is assigned tothe variable “new position”. For the first-time runthrough of theprocess, fixed pregiven values are utilized for these variables in theinitialization step 31. In a next step 34, the drives (6, 7) of the lampand the drive 20 of the collector lens are so driven that the drivesassume the values of the variable “new position”. Thereafter, ameasurement of the light power takes place with the diode 16 and areadout of the measured light power takes place as well as,subsequently, in a step 35, a further variable assignment takes place inthat the value of the measured light power is assigned to a variable“light power of new position”. In a next step 36, a decision inquirytakes place as to whether the value of the variable “light power of oldposition” (which likewise was assigned a value in the initializationstep) is less than the value of the variable “light power of newposition”. In the event this question is answered in the negative, then,in a step 37, a variable “actual step width” is assigned the value of avariable “countdown” and in a next step 38, the variable “light power ofnew position” is assigned the value of the variable “light power of oldposition”. In a next step 39, the value of a variable “position a” iscomputed as the sum of the variable “old position” and the product ofthe value of the variable “actual step width” and the variable“derivative of light power”. In a next decision step 40, a check is madeas to whether the value of the variable “actual step width” is greaterthan a pregiven limit value. If this inquiry is answered in theaffirmative, then the routine jumps with the new values back to theabove step 32 so that the subsequent steps are run through anew. If, incontrast, the inquiry in step 40 is answered with “false”, then the endof the routine is reached.

If, in the above-described step 36, the inquiry as to whether the valueof the variable “light power of old position” is less than or equal tothe value of the variable “light power of new position” is answered inthe affirmative, then, in step 41, the variable “actual step width” isassigned the value of a variable “count up” and, thereafter, in step 42,the gradient of the light power is measured. The details with respect tothe measurement of the gradient of the light power are described belowwith respect to the sequence diagram in FIG. 3. After the measurement ofthe gradient of the light power, the value of the measured gradient isassigned to the variable “derivative of light power” and, thereafter, instep 43, the value of the sum of the variables “new position” and theproduct of the variables “actual step width” and “derivative of lightpower” is assigned to the variable “position a”. Thereafter, the routinearrives also via this branch at the inquiry 40 as to whether the valueof the variable “actual step width” is greater than a limit value, and,in the case that this inquiry is answered in the negative, the routinearrives at the end of the routine and, in the case that this question isanswered in the affirmative, the routine also in this case returns tostep 32 downstream of the initialization step 31.

A method for determining the gradient of the light power is described ingreater detail in the following with respect to FIG. 3. In two firstassignment steps, the value of the variable “light power” is assigned tothe variable “actual light power” and the value of the variable “newposition” is assigned to the variable “actual position”. The values ofthese variables are either known from the previously run steps inaccordance with FIG. 2 or are determined in the initialization step 31according to FIG. 2. In two further initialization steps (53, 54), thevalues of the index variables (i) and (N) are determined. Thereafter,each individual drive (6, 7) of the lamps and the drive 20 of thecollector lens is sequentially displaced by a pregiven step width d_(i)and the light power impinging in each case on the diode 16 is measuredin a step 55. In a next step 56, the change of the light power ismeasured, that is, the difference of the variable “light power” and thevariable “actual light power” is computed. These steps are carried outfor all three drives separately one after the other. After thedifference values of the light power for the drive is present for allthree drives, the gradient of the light power (that is, a value of thevariable “derivative of light power”) is computed in step 37 as avectorial quantity. The value of the vectorial quantity “derivative oflight power” which was so computed is then used in steps 39 and 43 tocompute the new position “position a” which is to be controlled to.

In FIG. 4, a microscope according to the invention is shown having atransmitted-light illumination. Those components in the embodiment ofFIG, 4, which correspond to the components in the embodiment of FIG. 1,each have the same reference numeral increased by 100. The light, whichis emitted by a lamp 105, is collimated by a collector lens 109 and acollector mirror 117. A diaphragm 110 follows the collector lens 109 andis variable with respect to its aperture diameter. With respect to thedownstream optic, the diaphragm 110 is arranged so as to be conjugatedto the focal plane of the objective 104 and functions to adjust theilluminated field. A lens 111, which follows the field diaphragm 110,generates an image of the light source of the lamp 105 in the plane ofan aperture diaphragm 112. At the same time, the lens 111 images thefield diaphragm 110 to infinity. Two further lenses (113, 115) followbehind a deflecting mirror 114. On the one hand, the two additionallenses (113, 115) together image the plane of the aperture diaphragm 112in the rear focal plane of the transmitted-light condenser 125 and,simultaneously, image the field diaphragm 110 to infinity. Thetransmitted-light condenser 125 is integrated into the specimen table102. A so-called Köhler illumination can be adjusted in this embodimentin a manner known per se by adjusting the aperture diameters of thefield diaphragm 110 and the aperture diaphragm 112.

A partially transmitting mirror 123 is arranged rearward of the aperturediaphragm 112 for detecting the integral light power within theilluminating beam path. A small portion of the illuminating light iscoupled out via the mirror 123 and is focused via a downstream lens 124on a diode 116 integrated into the base of the microscope.

In this embodiment too, the lamp 105 is motorically adjustable in twomutually perpendicular directions perpendicular to the optical axis 119.For this purpose, the motorized drives (106, 107) are provided.Furthermore, also in this embodiment, the collector lens 109 isadjustable via a motor drive 120 in the direction of the optical axis119 for adjusting the illumination. The drive of the drive motors (106,107) for adjusting the lamp 105 and the drive of the drive 120 for theaxial displacement of the collector lens 109 again takes place via acontrol computer 122 as well as via an interface 121, which is providedon the microscope stand. The output signal of the diode 116 is suppliedto the control computer 122 also via the interface 121.

In the embodiment of FIG. 4 having the diode 116 integrated into theilluminating beam path, it is significant for the adjustment of the lamp105 in accordance with the method described with respect to FIGS. 2 and3 that the position of the aperture diaphragm 112 is conjugated to theposition of the entry pupil of the condenser 125 and, with respect toits aperture diameter, corresponds to the pupil diameter of thecondenser 125 while considering the magnification or demagnificationeffected by the two lenses (113, 115). Requirements of this kind are notpresent in the embodiment of FIG. 1; however, it is there necessary thatthe diameter of the light-sensitive region of the diode 116 is greateror equal to the diameter of the illumination field illuminated by theobjective 4.

The method according to the invention described above can, of course, beutilized not only for the adjustment of the lamp (5, 105) relative tothe illuminating beam path but, for a first adjustment, can also be usedto adjust the collector mirror (17, 117) relative to the collector (9,109). For this purpose, the lamp and the concave mirror can beiteratively adjusted alternately to maximum power at the diode (16,116). After a coarse preadjustment of the collector mirror,approximately three or four iterations are necessary in order to achievean optimal adjustment. Thereafter, when there is an exchange of lamps,only the lamp is adjusted perpendicular to the optical axis and thecollector lens (9, 109) is adjusted in the direction of the opticalaxis. An adjustment of the collector mirror (17, 117) is later notnecessary when there is an exchange of lamps.

The method of the invention was described above with respect to thegradient method for determining the position of the lamp with maximumlight power. The gradient method affords the advantage that it can, onthe one hand, be implemented simply and, on the other hand, leads to anoptimal adjustment with relatively few iteration steps. In lieu of agradient method, other algorithms are, however, conceivable, forexample, algorithms with which the individual drives are each drivensequentially until each individual direction of movement reaches themaximum of light power and these steps are repeated sequentially anumber of times until the absolute maximum as to detected light power isachieved.

It is understood that the foregoing description is that of the preferredembodiments of the invention and that various changes and modificationsmay be made thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

1-16. (canceled)
 17. A microscope comprising: a light unit for supplyinga light for transmission along an illuminating beam path devoid of abeam homogenizer; motor drives for adjusting said light unit relative tosaid illuminating beam path; a microscope objective defining a pupilplane; a four-quadrant detector mounted downstream of said pupil planefor detecting the light power of the transmitted light; an evaluationand control computer connected to said detector and functioning tosequentially drive said motor drives until a maximum of an integrallight power is measured with said detector; and, a specimen table andsaid four-quadrant detector being integrated into said specimen table.18. The microscope of claim 17, wherein said microscope defines anoptical axis along said beam path; and, said microscope furthercomprises: a collector optic mounted in said illuminating beam pathdownstream of said lamp unit; and, an additional motor drive fordisplacing said collector optic along said optical axis.
 19. Themicroscope of claim 18, wherein said evaluation and control computerfurther functions to apply a gradient method for locating said maximumof said light power by carrying out the following steps: beginning froma start position and determining the maximum gradient of the light powerin dependence upon a position change of at least one of said lamp unitand said collector optic; and, displacing at least one of said lamp unitand said collector optic in a direction of the maximum gradient of theintegral light power.